1. Field of the Invention
The present invention relates to a control apparatus or controlling a characteristic of a support unit, in other words, a suspension and/or a stabilizer, for supporting a vehicle body in order to restrain vibrations thereof.
2. Description of Related Art
To improve comfort while riding in a vehicle, a characteristic of support unit, of the vehicle body should be SOFT. Concretely, it is better that a damping force of the suspension is reduced, a spring constant of the same is small and soft, and torsion quantity of the stabilizer is reduced. On the other hand, to improve steering stability, the characteristic of the support unit of vehicle body should be HARD. Concretely, it is better that a damping force of the suspension is large, the spring constant thereof is large and hard, and torsion quantity of the stabilizer is larger.
A change-over system has been developed which has set the characteristic of the support unit SOFT (or MEDIUM between HARD and SOFT) in the normal running condition and changes over the characteristic to be HARD by driving change-over means for changing-over the characteristic of the support unit corresponding to necessity, such as variation, in the road surface condition or the posture of vehicle body. Such a system is disclosed in, for example, the Japanese Patent Application Laid-Open No. 60-47709, which measures the duration of acceleration not less than a predetermined value of vibration of the body, so that only when the duration is not less than a predetermined time, the damping force of the suspension is raised or the spring constant thereof is increased.
In such an example, poor comfort to ride caused by vertical vibrations of the vehicle body in the vicinity of the above-spring resonance frequency is detected on the basis of the duration of acceleration not less than the predetermined value, thereby controlling the characteristic of suspension to be harder. In this case, unless at least a half cycle period of time of the decision frequency in the vicinity of the above-spring resonance frequency passes, it is impossible to decide whether or not the characteristic of suspension is properly controlled, thereby delaying the control. Also, an initially large body shock caused when the vehicle runs over a large mound, or a large variation in the posture of vehicle body, is difficult to properly control.
Also, it is judged whether the vehicle is running on a bad road and the characteristic of the suspension or the stabilizer is changed to MEDIUM on the basis of the frequency component of below-spring vibration of the vehicle body or a vertical or lateral vibration pattern, thereby executing control to keep good comfort to ride and contact with a bad road. In this case, control cannot be executed even on the bad road until a reliable decision for the vibration frequency or the vibration pattern ends.
As mentioned above, at an initial stage of vibration of the vehicle body, it is not clear whether the characteristic of suspension or stabilizer is to be HARD or MEDIUM, and it takes much time to determine an optimum control parameter only from the information of vibration frequency. Also, in the following stage, when the vibration waveform represents a pattern of complicatedly superposing the above-spring vibration on the below-spring vibration, the following decision is imperfect and there is a possibility that the decision further delays, as disclosed in the Japanese Patent Application Laid-Open No.63-8010.